PROJECT SUMMARY Neuronal Ceroid Lipofuscinoses (NCLs) are a group of neurodevelopmental diseases categorized as autosomal recessive lysosomal storage disorders. Clinical features include retinopathy, intracellular accumulation of lysosomal ceroid and lipofuscin, seizures, motor decline and dementia. CLN3 disease (Juvenile Neuronal Ceroid Lipofuscinosis, JNCL) is one of the most common types of NCL, and results from mutations in the CLN3 gene on chromosome 16. Individuals with the CLN3 mutation show a consistent decline in cognitive functioning and verbal intellectual abilities over the course of later childhood and early adolescence. The precise neuropathological bases of this decline are not yet well understood and objective neurologic biomarkers (neuromarkers) of disease progression are not currently available. Yet, our preliminary data indicate that a good candidate for a biomarker of CLN3 disease that tracks with disease severity can be identified using high-density electroencephalography (EEG) in the context of auditory mismatch negativity experiments. Using these methods we have been able to show consistent declines in the P1 component of the auditory evoked response as CLN3 disease severity increases. Here we propose to further develop our understanding of auditory processing in children and young adults with CLN3 disease with a focus on validating a biomarker of the disease. Simultaneously we propose to use a mouse model of CLN3 disease with the same genetic mutation to identify an endophenotype that is shared in both patients and mice. We will also test whether the accumulation of autofluorescent lipopigments preferentially occur in specific subsets of interneurons and predict their subsequent loss as well as the hypertrophy of remaining interneurons. This three-pronged, convergence of techniques and approaches in both species has the potential to yield unique opportunities to understand the underlying neurophysiology of CLN3 mutations and their impact on auditory processing, as well as encourage testing of future treatments for CLN3 disease first in mice and secondarily in patients. This innovative approach, tying the patient neurophysiological markers to identical measures in the murine model of the disease will permit improved and more efficient pre-clinical development of novel therapeutics, improved measurement of disease progression in clinical trials, and with these advances, lead to improved outcomes for patients with CLN3 mutations.